The U.S.-Mexico War

Texas became an independent republic in 1836. Both the president of Texas, Sam Houston, and his good friend US president Andrew Jackson hoped to see a speedy US annexation. But Mexico refused to recognize the independence of its former province.

Polk, a Tennessee slave holder, won Northern support in his presidential bid by promising that the United States would take all of the Oregon Country up to Alaska from the British. But he quickly settled for half of that, dividing Oregon along the forty-ninth parallel, and leaving British Columbia to the British, infuriating many of Polk's supporters in the North. As soon as negotiations with Britain over Oregon were complete, Polk ordered US troops into an area between the Nueces and Rio Grande rivers that was claimed both by Mexico and Texas, openly antagonizing Mexico. After Mexicans fired on US soldiers, the president informed Congress that “American blood” had been shed on “American soil,” and asked for a declaration of war. The opposition Whig Party in Congress, terrified of being branded unpatriotic, swallowed their scruples and endorsed a war they believed to be unjust.^[2354]

Congress more than doubled the size of the army in response, to over 17,000 men, and authorized 10 temporary regiments.

On August 8, 1846, James K. Polk requested two million dollars from Congress to ne­gotiate an end to the war with Mexico. A Democratic congressman from Pennsylvania, David Wilmot, offered a proviso banning slavery from any territory gained from Mexico. The Proviso passed in the House, but not in the Senate, with voting falling along sectional rather than party lines. For the first time, the Democratic Party split over the issue of slavery, with many Northern Democrats making it clear that they would not condone the spread of slavery into lands that rightly belonged in the hands of free white men.

Expansion and sectional harmony were proving incompatible. Anti-slavery Democrats in the North began to desert the party for the new anti-slavery Free Soil Party. The opposition Whig Party, which opposed the war for reasons ranging from morality to self-interest, hoped to diffuse the growing sectional division by calling for an immediate end to the war without taking any territory from Mexico.

Still, success in Mexico inspired many Americans to broaden their horizons. A solid contingent of expansionist Democrats demanded the annexation of all of Mexico as spoils ofwar. Between October 1847 and January 1848—with the United States occupying Mexico City but no peace treaty in hand—avid expansionists gathered in mass meetings, calling for the immediate annexation of the entirety of Mexico. Members of Polk's cabinet were divided over how much territory to take from their defeated neighbor. Some, influenced by racism and convinced that the United States would be unable to govern densely populated Central Mexico, wanted a limited settlement along the lines of the present-day boundary between the two countries. Others, including Polk, hoped for vastly more of Mexico. A rogue dip­lomat named Nicholas Trist, who wished to see the United States withdraw from the country, negotiated a limited settlement with Mexico after being recalled from his duties by President Polk.^[2356]

The war officially ended in January 1848 when Mexico signed the Treaty of Guadalupe Hidalgo, transferring 500,000 square miles of Mexican land to the United States for 15 million dollars. Mexico lost her provinces of Alta California,

Nuevo Mexico, and parts of Tamaulipas, Coahuila, and Sonora, land which would become the American states of California, Nevada, and Utah, and parts of Texas, Arizona, New Mexico, and Colorado. David Pletcher has argued that much of this land might well have been gained from Mexico through negotiation, but the United States put far less energy into diplomacy with Mexico than it might have.^[2357]

Victory over Mexico was not so sweet for those living in the newly acquired ter­ritories. The Treaty of Guadalupe Hidalgo promised the new Mexican-American residents of the United States full citizenship rights. But racism and the unwilling­ness of local judges and juries to uphold the law in favor of Mexican Americans led to their political disenfranchisement.

With the 1848 Treaty of Guadalupe Hidalgo, the United States had become a continental empire. In name at least, the United States was in sole possession of the lands between the Atlantic and Pacific Oceans. In fact, the nomadic societies of the plains held title to much of the interior through binding treaties with the United States, and exerted physical control of vast stretches of the West. In 1851 the United States assigned territories to various plains nomadic societies to lessen the frequency of intertribal conflicts. Although the United States lacked the power to enforce compliance with the boundaries, the 1851 Treaty of Fort Laramie offered a tentative plan for the control of the plains.^[2359]

With European powers vanquished to the periphery of the continent, America's Manifest Destiny might have appeared complete in the 1850s. But the vast territo­rial acquisitions resulting from the U.S- Mexico War actually enflamed the desires of Democratic expansionists, who envisioned the United States encompassing Sonora, Cuba, Canada, and lands even further afield. They saw the successful conclusion of war with Mexico as legitimating a hemispheric destiny for the United States. On their own, some of these individual expansionists planned, and occasionally exe­cuted, attacks on other nations. These adventurers were called filibusters, and they operated without official sanction of any government, although often with the im­plied support of Democratic US politicians.

Among the most significant filibusters was a Cuban ex-patriot living in the United States named Narciso Lopez, who gained international attention as he re­peatedly tried to liberate the island of Cuba from Spain with the help of a small American Army in the late 1840s and early 1850s. Tennessee-born William Walker, a San Francisco newspaper editor during the California Gold Rush, became the most famous filibuster when he seized control of Nicaragua, which was divided by a Civil War, in the fall of 1855, and became first commander-in-chief of the republic's army. In July 1856, he became president of Nicaragua. For a brief period in the spring of 1856, Walker's Nicaragua was officially recognized by the United States. With his political hold on the country in decline soon after, the filibuster made a desperate effort to gain the political support of the American South. He reintroduced slavery into Nicaragua, where it had been illegal for 30 years. In May 1857 he lost a war to an army composed of Central Americans and the British, and was deposed.